The invention refers to a surgical instrument for aiming and hole forming purposes in connection with the implantation of locking nails or the like in bones.
As known, locking nails are bone nails which are introduced in the bone canal. The locking nails have transverse bores so that the locking nails can be fixed in the bone canal by bone screws inserted in transverse bores in the bones and through the transverse bores in the locking nail. By this the locking nails can be secured in the bone with respect to the axial and the torsional direction. Before placing the bone screws through the transverse bores in the locking nail corresponding bores must be made in the bone. It is clear that these bores must be coaxial with the transverse bores in the locking nail. However, it is not possible to determine the exact position of the transverse bores without specific means. Thus, aiming means are necessary for the application of locking nails. Most known aiming devices require a high energy radiation source, e.g. an X-ray source and receiving means and an image converter. In a known aiming device a drill sleeve serving for the guidance of the ddrill bit is attached to the housing or the frame of the X-ray source. Since the aiming device must be accommodated the different X-ray devices of the aiming device have to be designed in a different manner. This leads to relatively high costs.
Another known aiming device uses the proximal end of the locking nail as reference in order to determine the axial position of the transverse bores. The distance of the transverse bores from the proximal end is predetermined. Thus, it is only necessary to determine the axis of the transverse bores by means of the aiming device. A further aiming device can be used freehand by the surgeon (German utility model 84 17 428). A driving motor is accommodated in the aiming device and the chuck for retaining the tool, e.g. a drill bit, is transparent to X-rays. In this embodiment the drill bit is used as aiming means making use of the fact that the drill bit will appear on the image screen approximately as a point only if it extends approximately parallel to the beam direction. It is further necessary that the beam direction is coincident with the axis of the transverse bores. This can be determined by the image of the transverse bores. These are only circular when this coincidence is reached.
Finally, an aiming instrument is known including a drill sleeve attached to a gripping portion, the aiming means being connected to said drill sleeve in a defined position, the position of said aiming means between a radiation source and a radiation receiver being adapted to be illustrated on the screen of a converter (EPO application 0 201 737). Such an instrument also can be used freehand. The aiming means separated from the drilling sleeve has the advantage that a control and a correction of the aiming operation can be made also during the drilling operation. The known aiming device, however, requires a separate aiming element for the precise determination of the drilling axis, the aiming element being received by the drilling sleeve. The aiming element is defined by a pin made of material transparent to X-rays having a light-tight point or tip. By means of the aiming means and the aiming pin the drilling sleeve can be brought into an exact position against the bone. After a further adjustment by the aiming means a hole is formed by the drilling tool inserted in the drilling sleeve. The known aiming instrument, thus, requires two subsequent aiming operations which necessitate a certain time expense.